Tips for Properly Using Rock in a Drainfield

Always make sure rock used as distribution media is the right size, durable and clean

Jan 20, 2021 | by Sara Heger, Ph.D. |

Drainfield Septic System Installation Soil Featured

Drainfield Rock — Dirty rock has fines that can cause system malfunction by reducing the long-term acceptance rate of the underlying soil or media. Unwashed rock may be able to meet these specifications, but most rock needs to be washed to remove fine soil components.

Washed rock is used as distribution media in soil treatment area, media filters and in interceptor drains. It is obtained from quarries and gravel pits and is produced by screening, grading and washing to meet the desired specifications. In general, rock should be clean, sound and durable. Proper washing of the rock is critical to remove fine particles, such as silt and clay. If the aggregate washing process is inadequate, fine particles on the rock could ‘wash off’ the rock surface when the system is loaded with effluent. This could cause a layer of fines to accumulate along the infiltrative surface,

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